Study: Monkeys 'pay' for sex by grooming

In the primate world, sex is subject to the law of supply and demand

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Japanese Macaque monkeys groom each other, sitting in a hot spring in the snow at Jigokudani Wild Monkey Park in Yamanouchi, Nagano prefecture, central Japan. Male macaque monkeys pay for sex by grooming females, according to a recent study that suggests the primates may treat sex as a commodity.

Other experts not involved in the study welcomed Gumert's research, saying it was a major effort in systematically studying the interaction of organisms in ways in which an exchange of commodities or services can be observed — a theory known as biological markets.

Dr. Peter Hammerstein, a professor at the Institute for Theoretical Biology at Humboldt University in Berlin and Dr. Ronald Noe, a primatologist at the University of Louis-Pasteur in Strasbourg, France, first proposed the concept of biological markets in 1994.

"It is not a rare phenomenon in nature that males have to make some 'mating effort' in order to get a female's 'permission' to mate," Hammerstein said in an interview, likening the effort to a "fee" that the male pays.

"The interesting result of Dr. Gumert's research on macaque mating is that the mating market seems to have an influence on the amount of this fee," Hammerstein said.

Hammserstein said Gumert's findings indicate the monkeys are capable of adjusting their behavior to "different market conditions."

Gumert completed his fieldwork in February 2005 and first published his findings in the November issue of "Animal Behaviour," a scientific monthly journal.